Concentrations of megaliths, dolmens and stone labyrinths have been found (but little studied) throughout the Caucasus Mountains, including the unrecognized Republic of Abkhazia. Most of them are represented by rectangular structures made of stone slabs or cut in rocks with holes in their facade. These dolmens cover the Western Caucasus on both sides of the mountain ridge, in an area of approximately 12.000 square kilometres of Russia and Abkhazia. The Caucasian dolmens represent a unique type of prehistoric architecture, built with precisely dressed large stone blocks. The stones were, for example, shaped into 90-degree angles, to be used as corners or were curved to make a perfect circle. The monuments date between the end of the 4th millennium and the beginning of the 2nd millennium B.C.